Mirador viewer

SyntaxError: Unexpected token '<', "<!DOCTYPE "... is not valid JSON

{
  "manifest": {
    "error": "SyntaxError: Unexpected token '<', \"<!DOCTYPE \"... is not valid JSON",
    "id": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/756/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-334f7191-368c-4101-91f7-1fda322d8761",
      "cw-5ebe2c92-9cb1-44a6-8f06-d3e27b6bcef5"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-ea2601dd-ea6c-45ac-bae5-389915f4e830",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/756/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-5ebe2c92-9cb1-44a6-8f06-d3e27b6bcef5"
  }
}